The present invention relates to a rotary type compressor having a cylinder, an eccentric roller and a vane, which is applied to a refrigeration cycle in an air conditioner, a refrigerator or the like and, more particularly, to a compressor in which hydrofluorocarbon (hereinafter referred to as HFC) can be suitably used as a refrigerant in place of chlorofluorocarbon (hereinafter referred to as CFC).
As shown in a cross-sectional view of FIG. 2, a rotary type compressor usually comprises a cylinder 3, a roller 2 which eccentrically rotates in contact with the inner surface of the cylinder 3, and a vane 1 which has rectangular shape and extends along a guide groove of the cylinder 3 and is pushed by biasing means, e.g., a spring 4, so that the distal end of the vane 1 is pressed against the roller 2. Generally, the biasing means is introduced by a gaseous pressure or a hydraulic pressure, or resilient means such as a spring (the spring 4 in FIG. 2). Therefore, the distal end of the vane 1 is pressed against the outer peripheral surface of the roller 2, and the roller 2 rotates eccentrically while it is constantly pressed by the vane 1 in this manner.
In accordance with an increase of a gas compression ratio, a rotational speed of the roller is increased, and consequently, the sliding-contact surfaces of the vane and the roller tend to be worn by a remarkable degree. The roller is in sliding contact with the vane and the cylinder at its outer peripheral surface during rotation as described above. Thus, the roller is required to have properties making it resistive to wear and preventing it from imparting damage to the vane and the cylinder of the mating members.
CFC is used as a refrigerant for compressors. As well known, when CFC goes up to the stratophere, it is decomposed by irradiation of ultraviolet rays, thereby discharging chlorine which destroys the ozone layer. Such destruction of the ozone layer is globally considered as an environmental problem. Projects for totally abolishing use of CFC by the year 2000 have been formed, and development of an alternative refrigerant has progressed.
As an alternative refrigerant, HFC containing no chlorine, is the most promising. For example, 1,1,1,2 tetrafluoroethane (CH.sub.2 FCF.sub.3) known as R-134a may be raised. Use of such kind of fluorocarbon involves the following problems with respect to compressors when it is compared with use of the conventional CFC even though HFC does not as adversely affect the environment.
1. A lubricative property of the refrigerant is inferior. PA1 2. The compression ratio must be increased, and consequently, the load acting on the roller and the vane becomes greater. PA1 3. A hygroscopic property of the refrigerant is larger. PA1 4. A lubricative property of a lubricant is inferior. PA1 5. A hygroscopic property of the lubricant is larger. PA1 1. Wear of the sliding contact members increases. (Wear of the roller and the vane particularly increases.) PA1 2. The tendency of seizure of the roller and the vane is higher. PA1 (1) Graphite dispersed in at least one of a roller and a vane (only a roller in case of the present invention) at not lower than a predetermined area ratio maintains lubrication conditions at a predetermined level or higher. Carbides which are hard and less likely to adhere when they contact each other than with metal (especially, MC type carbides of a high hardness which are chemically stable), nitride particles of TiN, NbN and so forth which have lower affinity with Fe (i.e., a mating material) than the carbides, and crystallized eutectic structure including iron phosphide, are distributed in at least one of the members at predetermined area ratios or higher. Further, these substances are distributed while projected from the metallic matrix surface owing to differences of the wear resistances, thereby decreasing metal-to-metal contact which easily causes adhesion. Thus, adhesion is restrained to occur with respect to both the members. PA1 (2) The roller material is strengthened by quenching/tempering treatment of the matrix and by including not less than a predetermined area % of crystallized eutectic structure having iron phosphide of a high hardness. Consequently, the roller material is prevented from being partially removed forcedly in the above-described manner. PA1 (3) The vane material contains carbides of not larger than a predetermined size, and includes TiN and NbN which have low affinity with Fe in the mating material so as to decrease an attacking influence on the mating material.
Under the above-described circumstances, the following problems are caused in relation to sliding contact members such as the cylinder, the roller and the vane.
More specifically, since the conventional CFC contains chlorine, it forms a stable protective film (chloride) on the surfaces of the sliding contact members so as to provide the sliding contact surfaces with good wear resistance and anti-seizure properties. On the other hand, HFC of an alternative fluorocarbon, contains no chlorine. Therefore, unlike with use of CFC, an advantageous effect of improving the wear resistance and anti-seizure properties cannot be expected, and HFC involves a different problem in practical use.
In order to solve the problem, it is effective for a material of the vane to has increased hardness and to increase an additive amount of hard carbides. As this type of material, for example, JP-A-5-9660, JP-A-5-171376, JP-A-5-279809 have been known. With such a material, the wear resistance and anti-seizure properties of the vane can be improved to some extent.
Conventionally, the roller has been made of cast iron by continuous casting, eutectic graphite cast iron, or Cu--Cr-system, Cu--Mo-system or Mo--Ni--Cr-system low alloy cast iron. Because the roller involves more restrictions regarding the cost than the vane, the above-mentioned cast irons are most suitable. In such a case, it is effective to increase hardness and strength of the matrix and to make graphite finer. This type of material is disclosed in, for example, JP-B2-60-1943.
According to the foregoing method of improving the vane, the material contains large amounts of expensive alloying elements resulting increased the cost. Further, according to such way, although an amount of wear of the vane itself is decreased, an attacking influence on the roller is increased. Consequently, wear of the roller is increased, thus easily deteriorating the anti-seizure property of the roller.
Also, according to the above-described method of improving the roller, improper increases in hardness and strength of the matrix thereof cause an attacking influence on the vane to increase wear of the vane resulting in deteriorating the anti-seizure property of the vane.
In other words, anti-seizure and wear resistance properties cannot be fully improved by solely improving either one of the vane and the roller. It is important to improve these properties by a conformable optimum combination of a vane and a roller.